Lab Resistivity testing on coarse aggregate

[chankawai]

I need to find a way (in the lab) to test the resistivity for aggregate having a nominal size of 3/4" with very little fines. The material will not conform to AASHTO T 288. Does anybody know of a way to do this?

 

[civilperson]

Resistivity to electric current or to sulfides and salt attack?

 

[chankawai]

electrical

 

[civilperson]

Need to go to the stockpile or pit where this material is from to get probes at a respectable distance apart. (lab dimensions will be too rough, =/- 50%).

 

[MRM]

That spec is for minimum resistivity in the lab. It's used as a lower bound for resistivity. The idea being a soil with lower resistivity has a higher corrosion potential. If you're working with aggregate, the resistivity is likely to be very high. Because of this, aggregate itself usually wouldn't be that corrosive. The only case that I think it could be is if the aggregate is saturated in the field and the pore water has a high concentration of soluable salts.

 

[civilperson]

Resistivity is a necessary parameter in the design of grounding for electrical substations. Low resistivity gives a safe ground system with larger grid of buried copper conductors and maybe no need for drilling a well for grounding purposes.

 

[MRM]

I wouldn't count on open graded, unsaturated aggregate having good enough properties to place a ground mat within it. In fact, this material is typically used to eliminate step potential when it is a concern.